1. Field of Invention
The present invention relates to a projector for projecting and displaying an image.
2. Description of Related Art
In a projector, image light representing an image is formed from illumination light by the use of an electro-optical apparatus, and an image is displayed by projecting the image light. As the electro-optical apparatus, an optical modulation device for modulating the illumination light according to image information and emitting the image light representing the image is used. As an example of a micro-mirror-type optical modulation device, a micro-mirror-type optical modulation device, such as a Digital Micro-mirror Device (a registered trademark of Texas Instruments, Inc.; hereinafter referred to as xe2x80x9cDMDxe2x80x9d) can be given.
The DMD has a plurality of micro-mirrors corresponding to a plurality of pixels constituting the image. The inclination of the micro-mirrors varies with image information, and the micro-mirrors reflect light according to the inclination thereof. Of the light reflected by the micro-mirrors, the light reflected in a predetermined direction is used as image light. That is, the DMD is an electro-optical apparatus of a type which controls the direction of reflection of light entered at a predetermined angle so as to form image light. Therefore, when an optical modulation device such as the DMD is used as an electro-optical apparatus for a projector, in order to realize a high-precision and bright image, illumination light applied to the optical modulation device may preferably be entered at the highest possible precise predetermined angle.
The illumination light emitted from an illuminating optical system, however, actually has various incident angles. For this reason, the illumination light having an angle beyond the allowable range of a predetermined incident angle cannot be used as image light. Consequently, there is a problem in that illumination efficiency of the illuminating optical system is deteriorated. In addition, this problem also occurs in optical modulation devices for controlling the direction of emission of illumination light applied to a light application surface, including a plurality of pixels, for each pixel according to image information to thereby emit image light representing an image.
It is an aspect of this invention to provide a technique for achieving an increase in illumination efficiency of an illuminating optical system in a projector using an optical modulation device for controlling a direction of emission of illumination light applied to a light application surface, including a plurality of pixels, for each pixel according to image information to thereby emit image light representing an image.
According to the present invention, a projector, may include: an optical modulation device for controlling a direction of emission of illumination light applied to a substantially rectangular light application surface, including a plurality of pixels, for each pixel according to image information to thereby emit image light representing an image, an illuminating optical system for emitting the illumination light so that the central axis of the illumination light applied to the light application surface enters the light application surface at a predetermined angle, and a projection optical system for projecting the image light emitted from the optical modulation device.
The illuminating optical system may include a light source, and a light-transmitting rod through which the light emitted from the light source passes, at least a part of the light passing while being repeatedly reflected by an inner surface of the light-transmitting rod. The light-transmitting rod has a shape such that a sectional area perpendicular to the central axis of the light-transmitting rod monotonically increases from the incident side to the emitting side.
According to the above projector, the angle of the light passing through the light-transmitting rod to enter the inner surface of the light-transmitting rod (incident angle) gradually increases each time the reflection is repeated, so that the angle of light relative to the central axis of the illumination light emitted from the light-transmitting rod can be reduced. Consequently, the angular distribution of the illumination light having various angles can be reduced. This can increase the precision of the incident angle of the illumination light applied to the light application surface of the optical modulation device, so that the illumination efficiency of the illuminating optical system can be increased, and a bright projected image can be displayed.
Here, the light-transmitting rod may have a shape such that the size of each side of a cross section perpendicular to the central axis of the light-transmitting rod linearly increases from the incident side to the emitting side. Thus, the light-transmitting rod can be manufactured relatively easily.
In the above projector, at least an outline shape of an emitting surface of the light-transmitting rod may preferably be a quadrilateral having first and second diagonal lines of different lengths. When the illumination light emitted from the light-transmitting rod obliquely enters the light application surface at the predetermined angle, the quadrilateral may preferably be set so that the ratio of two diagonal lines of a quadrilateral illumination area to which the illumination light is applied comes closer to 1 than the ratio of the lengths of the first and second diagonal lines.
This allows the outline shape of the illumination area to approach the light application surface having substantially a rectangular shape, even if the illumination light obliquely enters the light application surface at the predetermined angle. Therefore, illumination efficiency of the illumination light applied to the light application surface of the optical modulation device can be further increased.